Inherited Disorders and Birth Defects

Full Trisomy 9 Recurrence Risk

07/12/2007

Question:

We just obtained the results from the chromosomic analysis of our baby girl (lost at 18 weeks): Full trisomy 9 in all the cells, not exactly what we expected (we suspected Trisomy 18). Our Doctor said that there is a a recurrence risk of 3-5 percent and that I should not worry about it, but perhaps opt for early testing in my next pregnancy. Any thoughts? Thank you.

Answer:

First, let me say that I am so sorry for your loss.

Trisomy 9 means that there were 3 copies of chromosome 9 in all the cells instead of the normal number of 2 copies. Almost all pregnancies where there is a full trisomy (an extra chromosome) miscarry. The trisomies that may result in a live born child are trisomy 21 (Down syndrome), trisomy 18 and trisomy 13.

About 10-15% of all pregnancies end in a miscarriage. Of these, about 50% will be due to a chromosome abnormality and most of these abnormalities are trisomies - so they are very common in miscarriages.

The vast majority miscarriages that are due to a chromosome abnormality happen to parents that have normal chromosomes and the chromosome abnormality happened as a sporadic event when the egg or sperm was formed. I would assume this is the case for you and your partner and that the chance that this would happen again is very low. However, you may wish to consider prenatal testing in a future pregnancy for reassurance that this has not happened again.

You may want to talk to a geneticist or genetic counselor to discuss this in detail and answer any additional questions you may have. You can locate a genetics center near you at the National Society of Genetic Counselors recourse center website below.

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